3.8. Assemble in MRI Compatibility Mode: -M

The -M or -mri option selects MRI compatibility mode. This
changes the syntax and pseudo-op handling of as to make it
compatible with the ASM68K or the ASM960 (depending upon the
configured target) assembler from Microtec Research. The exact nature of the
MRI syntax will not be documented here; see the MRI manuals for more
information. Note in particular that the handling of macros and macro
arguments is somewhat different. The purpose of this option is to permit
assembling existing MRI assembler code using as.

The MRI compatibility is not complete. Certain operations of the MRI assembler
depend upon its object file format, and can not be supported using other object
file formats. Supporting these would require enhancing each object file format
individually. These are:

global symbols in common section

The m68k MRI assembler supports common sections which are merged by the linker.
Other object file formats do not support this. as handles
common sections by treating them as a single common symbol. It permits local
symbols to be defined within a common section, but it can not support global
symbols, since it has no way to describe them.

complex relocations

The MRI assemblers support relocations against a negated section address, and
relocations which combine the start addresses of two or more sections. These
are not support by other object file formats.

END pseudo-op specifying start address

The MRI END pseudo-op permits the specification of a start address.
This is not supported by other object file formats. The start address may
instead be specified using the -e option to the linker, or in a linker
script.

IDNT, .ident and NAME pseudo-ops

The MRI IDNT, .ident and NAME pseudo-ops assign a module
name to the output file. This is not supported by other object file formats.

ORG pseudo-op

The m68k MRI ORG pseudo-op begins an absolute section at a given
address. This differs from the usual as.org pseudo-op,
which changes the location within the current section. Absolute sections are
not supported by other object file formats. The address of a section may be
assigned within a linker script.

There are some other features of the MRI assembler which are not supported by
as, typically either because they are difficult or because they
seem of little consequence. Some of these may be supported in future releases.

EBCDIC strings

EBCDIC strings are not supported.

packed binary coded decimal

Packed binary coded decimal is not supported. This means that the DC.P
and DCB.P pseudo-ops are not supported.

FEQU pseudo-op

The m68k FEQU pseudo-op is not supported.

NOOBJ pseudo-op

The m68k NOOBJ pseudo-op is not supported.

OPT branch control options

The m68k OPT branch control options--B, BRS, BRB,
BRL, and BRW--are ignored. as automatically
relaxes all branches, whether forward or backward, to an appropriate size, so
these options serve no purpose.